M81 More than just the ATX power supply (no replies)

Hi

I have the latest stable version of Marlin running on a Ramps board. I am using the single output to control an ATX power supply. The ATX power supply is only being used for the Heatbed. I have a different power supply connected to the other 12 volt input for the motors and hotend.
I had a strange problem where just before finishing a print both heaters showed that they had been turned off. For some reason Matter control sent the M81 command before it finished the print. This should have just turned off the heatbed but when examining the log file I saw this...

->N53688 M105*39 [4234.121]
<-ok T:210 /210 B:58 /65 @:63 B@:127 [4234.124]
->N53689 M81*27 [4234.124]
<-echo:busy: processing [4236.156]
<-ok [4238.925]
->N53690 M105*46 [4238.925]
<-ok T:209 /0 B:58 /0 @:0 B@:0 [4238.942]

Shaded blue you can see that both hotend and bed have temps set. After the M81 both have temps set to 0.

I did not see this funstionality mentioned in the doc.
Any thoughts on this?

I am still trying to figure out why when the M81 was sent the bed already seemed to be off - see the temp is only 58 and should be 65